ICRF-187 protected against the chronic cardiomyopathy induced by the administration of doxorubicin to beagle dogs. This protection continued when the total dose of doxorubicin was increased up to 3 times the usual dose that would produce cardiomyopathy in animals not pretreated with ICRF-187. ICRF-187 allowed full doses of doxorubicin to be given to beagle dogs for up to two years without producing cardiomyopathy, thus raising the possibility of using a similar mode of treatment in patients with cancer.